Canadian Airgun Forum

Hi Alex,

Most of the information I've gotten is from the experts here and on other forums. The sails are just steel or aluminum washer like you see in the example in Daryl' reply below (although the valve parts in the photo are from a Hatsan BT65 I believe). I made mine from washer in my parts bins because I couldn't find anything close at the local hardware stores (I did find some fender washer that were close but they were thick stainless still and the OD was very large so I would have to grind them down a lot). For their purpose, I think aluminum washers are fine and much easier to re-size if you need to. The washers I tried varied in thickness from .070" to .150" (I think this small variation in thickness only varies the preload of the spring a little so is not too critical). The ID of the washers I tried were: .360", .350". .343". The .350" and .343" seemed to work the best so far. I'm still trying to find the right combination.

Like I said, the "Sails" are just washer and look like the one Daryl's photo below. I'll take some photos of mine and try to post it later. Hope this helps.

Hi Dayrl,

Thanks for the information on the stems. I had read Sterne's great test on AT44 stems and power settings and Walter's suggestion about the "sail", (which is what got me started on this project). I think I am still a little unclear about the relationship between the stem size and the sail size. I know that the standard .100" stem uses a lot of air (one reason it gives much more power) but I thought that by using a sail, the size of the stem didn't matter because you are controlling the amount of air flowing through the valve with the size of the sail, not the size of the stem. Plus with the sail you also get the added benefit of a more effective stem. I think it has a similar effect as a debounce device. I could be wrong on this and the amount of air flow through the valve is controlled by both the size of the stem and the size of the sail.

I've tried a few more variables but so far not getting the 50 shots within 4% that I want so I think I'm going to try turning down a .150 stem and try a few different sizes to see if that will help me get to where I want to go. It will be a while before I can get that done and run some tests so for now it looks like the settings used in Test 7 and 8 were the most usable. Test 7 had more available shots so if you were shooting at closer ranges like 25 yards, that would be a good setting. If you were shooting at 50 yards or more the settings used in test 8 might be better.

Test 6 looked good with the total number of shots (70) with 36 within 4% but there were so may non-usable shots at the beginning of the string.

If you start your string at 2,500, 2,600 or 2,700 psi instead of 3,000, you might be starting in the meat of the string, without the waisted pellets to get it down to that level.

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Best Wishes
Daryl

I went through all the same experiments with my Pneuma and in the end I bought a regulator. However you learn so much doing the experimenting, it was totally worth it. Good luck.

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If I had only one wish, it would be to be able to "unsay" things.

Thanks for the suggestion Daryl. Those are some of the variables I've been trying. Most of my early shot strings, started too low (688 fps). Since decreasing the starting fill pressure, increases the fps of the early shots and increasing the hammer preload increases the fps of the early shots, that's what I've been testing. 180, 170, 160, 150 bar fills at different power settings (2 CCW, 4 CCW, 5 CCW, 6 CCW). The 170 bar fill with the PA at 4 CCW, got a great shot count (80 shots), starting and ending fps was very close (719 & 718) but the max high was 2/3 the way through the string. I started trying different combinations of preload and fill pressure but never could find the right combination.

Joe, I agree and I'm glad I tried this mod because it was a good learning experience. I may try a couple of more times, then try playing with a resized stem (maybe .120") but if that doesn't get me the results I'll have to start thinking about a regulator. I bought a second air tube so if I get a regulator, maybe I'll put it in the new tube and put the .120" stem in the second tube and use it as my "low power/short range" tube that I can get a lot more shots out of.